A mechanical vibrator of the general above-described type is disclosed in German Patent Application No. P 34 22 005.4-35 in connection with a method and apparatus for the derivation of a course deviation signal for an earth satellite in orbit by means of an earth horizon sensor. DE-OS No. 20 35 314 discloses another satellite-related application for such a beam chopper used in an infrared telescope which operates with cooled infrared sensors. Since these sensors only deliver signals in the microvolt range and such small d-c signals can be amplified only with difficulty, it is necessary to chop the signal. Such chopping is advantageously accomplished by chopping the incident radiation by means of a beam chopper. This chopping must be accomplished completely uniformly, i.e., the times during which the radiation strikes the infrared detector must be exactly as long as the respective dark phases. A secondary-mirror tilting device serving similar purposes for a mirror telescope is known, for example, from DE-OS No. 32 13 076.
Due to the small power loss required in satellite applications, such beam choppers are operated at resonance, i.e., at the resonance frequency of a mass/spring system.